In the past, the fabrication of bimetallic bearings has been plagued by the difficulty of obtaining a good bond between the dissimilar metals that make up the bearing. Conventional fabrication techniques call for a bearing metal piece to be placed in a form or mold and the dissimilar metal, in a molten state, to then be poured into and around the bearing metal piece. For many combinations of metals, this type of process has produced a bond of satisfactory quality.
Unfortunately, it has been observed that when the bearing metal piece is bronze and the dissimilar metal is molten aluminum, the bonding between the metals is of poor quality. It is believed that, when the molten aluminum comes in contact with the bronze, the lead which is present in the bronze is converted to a gaseous state. More specifically, the poor quality of the bonding between the metals is caused by the presence of molten lead, aluminum and liberated lead gas with no place to escape.
In other words, the molten lead and lead gas are present to an unacceptable degree in a band between the aluminum and bronze. This lead outgassing coupled with the inability of molten lead to escape from between the aluminum and bronze has made it necessary to abandon conventional fabrication techniques in favor of joining the bronze and aluminum components by soldering. However, when soldering has been utilized, it has proven to be expensive due in part to poor production yields. Soldered joints can also de-bond at some operating conditions.
Among the casting techniques that have been proposed, Monnot U.S. Pat. No. 929,778 discloses a film coating on an iron or steel object by dipping the iron or steel object in a bath of super molten copper. A further coating is then formed by contacting the surface defined by the film coating with a molten aluminum at substantially ordinary casting temperatures to create a layer of a desired thickness. In this manner, Monnot produces a compound metal body having a core or iron or steel, a copper film coating, and a layer of aluminum.
As for other bearing and casting methods, Jones et al U.S. Pat. No. 1,789,979 discloses lining a shell formed of steel by fluxing the shell with a solution of borax after which the shell is dipped into a mass ofmolten bearing metal such as babbitt. Whitfield et al U.S. Pat. No. 2,453,772 discloses coating articles having a copper base with an aluminum or aluminum alloy by first coating the copper surface with a thin skin or layer of a metal of the class consisting of nickel, iron, cobalt, manganese and chromium. Further, Niimi et al U.S. Pat. No. 3,841,386 discloses dipping a solid beryllium workpiece in a molten bath of copper after which the workpiece is quickly dipped in a molten bath of aluminum, set in a mold, and molten aluminum is poured into the mold to complete the casting.
Despite these and other efforts, it has remained to overcome the problems of successfully producing a bronze and aluminum bearing without the need for soldering. The present invention is directed to overcoming these problems and accomplishing the resulting objects by providing a unique new method of making a bearing.